Instantaneous beamforming exploiting user physical signatures

ABSTRACT

A communication system where a central node (base-station or access point) communicates with multiple clients in its neighbourhood using transparent immediate beam-forming. Resource allocation and channel access is such that the central node does not necessarily know when each client starts its transmission. Receive beam-forming in such a system is not possible, as beam-forming coefficients for each client should be selected according to the particular channel realization from that client to the central node. Each client is detected early in its transmission cycle, based on either a signature that is part of the physical characteristics unique to that client, or based on a signature that is intentionally inserted in the clients&#39; signal, and accordingly adjusts its beam-forming coefficients.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/585,128 entitled “INSTANTANEOUS BEAMFORMING EXPLOITING USERPHYSICAL SIGNATURES,” filed May 2, 2017, which is a non-provisionalfiling of, and which claims benefit under 35 U.S.C. § 119(e) from, U.S.Provisional Patent Application Ser. No. 62/330,687, filed May 2, 2016,entitled “INSTANTANEOUS BEAMFORMING EXPLOITING USER PHYSICALSIGNATURES,” each of which is hereby incorporated by reference herein inits respective entirety.

FIELD

The present invention discloses methods to realize Radio Frequency (RF)beam-forming.

BACKGROUND

Receive RF beam-forming is widely used as a mechanism to improve signalstrength and/or reduce multi-user interference. On the other hand, inmany scenarios, user scheduling for uplink transmission is not fullypre-determined. This is referred to as Random Access. WiFi systems are anotable example in this category. Other examples include “emerging M2Mand IoT applications”. Hereafter, methods and systems described hereinwill be explained in the context of WiFi systems, such 802.11g and802.11n.

In setups using Random Access, clients access the uplink channel withoutprior coordination. This means, the Access Point (AP) does not have anyprior knowledge about the identity of the client which will next accessthe uplink channel. In this configuration, AP can determine the identityof the client sending in the uplink only after the preamble of thecorresponding uplink packet is received and is successfully decoded.Hereafter, this feature is refereed to as Uplink Client Anonymity. Thisshortcoming makes it difficult for the clients who are in deep fade toeven establish the link. For those clients that the uplink signal isstrong enough to be heard by the AP (establish the link), being subjectto deep fades will reduce the throughput and increases the delay. AP'sare typically unable to adjust its antenna (beam-forming) pattern toprovide each client with a better reception during this stage.

Due to Uplink Client Anonymity, Transparent Beam-forming in the uplinkis more challenging as compared to the case of downlink. As aconsequence, prior art in Transparent Beam-forming is limited todownlink transmission. In particular, some prior art relies on observingthe packet-level error behavior in the downlink, and accordinglydetermines a transmit (downlink) antenna pattern for a particularclient. The error behavior is gauged by examining multiple antennapatterns and selecting the one that minimizes the Frame Error Rate(FER), wherein FER is measured by counting the number of retransmissions(for any particular client in conjunction with the examined transmitpatterns). As a result, methods based on the prior art are slow, andinefficient. Another disadvantage of such prior art techniques stems intheir inherent reliance on observing erroneous packets to guide theirbeam-forming decisions. In other words, they can offer improvements onlyafter several downlink packets are communicated in error. Thisshortcoming results in delay and reduces the throughput. Anothershortcoming of prior techniques is that they are limited to downlinkbeam-forming, while beam-forming in the uplink is generally moreimportant. The reason is that, in the downlink, an AP typically relieson better power amplifiers as compared to that of resource limitedmobile clients. This inherent mismatch (downlink vs. uplink linkquality) means that Transparent Beam-forming is actually more importantfor use in the uplink, yet solutions do not exist.

One reason that Transparent Receive Beam-forming has not been used innetwork setups using Random Access is that beam-forming coefficients foreach client should be selected based on the particular channelrealization corresponding to that client, and the AP does not know whichclient will next occupy the uplink channel.

A challenge in Uplink Transparent Beam-forming concerns computation andtracking of the proper beam-forming weights for each client. Thesefeatures limit the abilities of the AP in adjusting its receivebeam-forming weights in a timely manner in order to provide the bestreceive gain for the particular client that is occupying the uplink. Onthe other hand, in transmit beam-forming, the access point is aware ofthe identity of the client that will be next serviced in the downlink(prior to starting the transmission), and accordingly, can adjust itsbeam pattern according to the particular client.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an embodiment of a wireless network using the receivebeam-forming apparatus described herein such that the beam-formingoperation is transparent to legacy clients.

FIG. 2 is a general receive beam-forming apparatus wherein each of the Kreceive chains is equipped by M antennas.

FIG. 3 is an implementation of antenna beam-forming weights, whereinonly the signal phase is changed by 180′, while signal magnitude remainsthe same.

FIG. 4 shows a beam-forming apparatus with its associated control unit.

FIG. 5 shows an embodiment for generating 0/180 degrees phase shifts.

FIG. 6 is another embodiment wherein 0/180 degrees phase shifts arecascaded with RF attenuators to provide some additional degrees offreedom in adjusting antennas beam-forming weights.

FIG. 7 shows an example of Plus-Minus Phase Vectors used in theformation of Physical Signatures corresponding to M=8 (# ofantennas/chain), K=1 (# of chains), and S=4 (# of signature vectors).

FIG. 8 shows a WiFi preamble, indicating the operations that arecompleted prior to the start of the Long Training Sequence (LTS), suchthat channel measurements are performed for the actual antennaconfiguration that will be in effect.

FIG. 9 shows another embodiment wherein each group of M antennas isequipped with two sets of phase shifters operating in parallel.

FIG. 10 shows a pictorial view of the switching between the twobeam-forming sets related to FIG. 9.

FIG. 11 shows the pictorial view of a network setup equipped withEnhanced Transparent Instantaneous Beam-forming.

FIG. 12 shows another embodiment wherein each group of M antennas isequipped with two sets of beam-former phase shifters operating inparallel.

FIG. 13 shows a pictorial view of an embodiment of the disclosedEnhanced Transparent Instantaneous Beam-forming structure forsuperimposing a sinusoidal signature signal on the RF signal generatedby the underlying legacy transmitter.

FIG. 14 shows a pictorial view of an embodiment of the disclosedEnhanced Transparent Instantaneous Beam-forming structure forsuperimposing a sinusoidal signature signal containing modulated data onthe RF signal generated by the underlying legacy transmitter.

FIG. 15 shows a pictorial view of an embodiment of the disclosedEnhanced Transparent Instantaneous Beam-forming structure forsuperimposing a spread spectrum signature signal on the RF signalgenerated by the underlying legacy transmitter.

FIG. 16 shows the pictorial view of the control mechanism in EnhancedTransparent Instantaneous Beam-forming.

FIG. 17 shows a method of changing the selected channel for the reasonof limiting the impact on other users who are sharing the spectrum andare not part of the network, i.e., do not contain the superimposedsignature signal.

FIG. 18 shows an embodiment wherein, in addition to the output of thecombiner, the outputs of individual antennas are monitored towardsextracting information about the individual signals separately.

FIG. 19 shows a pictorial view of an embodiment for sharing theAuxiliary Receiver.

FIG. 20 shows a pictorial view of another embodiment for sharing theAuxiliary Receiver.

DETAILED DESCRIPTION

Described herein are systems and methods using multiple antennas withbeam-forming capability per receive chain, suitable for use with legacyWiFi systems. For example, considering an 802.11n legacy system withsome number of receive chains (e.g., four chains may be used as iscommon in many systems, but higher orders may be used), each of thereceive RF ports may be fed by a group of antennas (in one embodiment,eight antennas are used), wherein each such group of antennas isequipped with beam-forming among its members. Beam-forming patterns foreach such group (of, e.g., eight) antennas will be determineddynamically and transparently to improve the signal quality. Note thatbecause the receive beam-forming is additional and transparent to legacysystems, it may be combined with any other layer of beam-forming orMultiple-Input Multiple-Output (MIMO) processing that may be appliedacross the receive chains as part of the receive processing in theunderlying legacy receiver. Hereafter, such a beam-forming operationwill be called Transparent Beam-forming as it is designed to remaintransparent to the operation of the underlying legacy transceiver.

It is also desirable that antenna pattern is readjusted per receivedpacket according to the client that has initiated the correspondinguplink transmission. This will reduce the chances of any packet beingreceived in error.

Methods of this invention for Instantaneous Beam-forming detects eachclient, very early in its transmission cycle, based on a SignatureVector that is part of the physical characteristics unique to thatclient. It also finds and tracks the best antenna pattern for eachclient, and tabulates it together with some other information related tothat client.

As mentioned, the AP faces the challenge of computing/tracking thebeam-forming weights for different clients. It is desirable that receivebeam-forming can be performed early enough during the uplink receptionsuch that the beam-forming weights can be adjusted without losing anypackets. It is also desirable that the transmit beam-forming weights canbe learned (and be associated with their respective clients) as part ofthe uplink beam-forming procedure, and are then applied during thedownlink transmission according to the client that is being serviced.

In many such Random Access systems, the transmission starts with asynchronization signal followed by training signals to be used forchannel estimation/equalization. In the uplink beam-forming, the systemsand methods described herein provide rapid classification andidentification of the active client (including operations related totracking of antenna weights), and accordingly, adaptation of the antennaweights is performed in a manner that the quality of the channelestimation is not compromised. Note that the antenna pattern is inessence part of the uplink channel, and consequently, it affects thechannel estimation. Thus, in some embodiments, beam-forming is appliedearly enough such that the training signals can be effectively used bythe access point to estimate the channel, including the role of thenewly applied beam-forming pattern in the estimation of the overallchannel.

Methods of various embodiments described herein, which are generallyreferred to herein as Transparent Instantaneous Beam-forming (TIB) maybe used without modifying the underlying WiFi standard. TIB is wellsuited to be integrated in WiFi access points to improve link quality inboth directions, while communicating with legacy clients, which remaincompletely transparent to such a beam-forming operation.

The systems and methods may be used herein in combination with existinglow cost WiFi chip sets, while adding features (through simple hardwareadditions) that enhance the overall performance. Along this line,methods described herein include an Enhanced Transparent InstantaneousBeam-forming (E-TIB) scheme. Recall that TIB was designed to be fullycompatible with the underlying standard. This means, only the AP wasequipped with TIB, and clients remained unaware of the AP's beam-formingcapability. In some applications, as described more fully herein below,both sides of the link belong to the same vendor, and can be slightlymodified, while still benefitting from available WiFi chip sets. This isachieved using Enhanced Transparent Instantaneous Beam-forming (E-TIB).

Transparent Instantaneous Beam-Forming, or TIB.

Many embodiments described herein utilize signatures, called PhysicalSignatures hereafter, to distinguish clients from each other. Example ofPhysical Signatures include: (1) Frequency mismatch, (2) Channelmagnitude and/or phase over frequency, and (3) Channel magnitude and/orphase over different antenna patterns, (4) Angle of arrival, and (5)Doppler frequency. One embodiment described herein uses PhysicalSignatures corresponding to values of received energy over a few knownantenna patterns. Physical Signatures are arranged in a vector,hereafter called the Signature Vector. The signature vector is a set ofmeasured signal levels, where the signal levels correspond to differentbeam-formed signals that are formed during a training period. Thedifferent beam-formed signals are formed using a set of beams referredto herein as signature beams.

Receive RF beam-forming entails combining RF signals from multiplereceive antennas after proper adjustments in their relative gain and/orphase values. It is desirable to achieve a good portion of the possiblereceive beam-forming gain using a simple hardware structure. The presentdisclosure describes beam-forming strategies, which are not only simpleand cost effective with a good performance, but are also compatible withextraction of users' Physical Signatures as described herein.

In a preferred embodiment, each antenna is connected through anadjustable weighting element by which an analog weight coefficient (AWC)may be implemented. The set of AWC for a given beam may be referred toas an AWC vector. In some embodiments, the adjustable weighting elementmay comprise a phase shifter with two selectable phase values, 0 or πThe weighting elements may be connected to a signal combiner to generatethe beam-formed signal. As a result, M antennas can generate 2M antennapatterns (or beam-formed signals), specified by vectors of size M withelements 1 and −1, representing a phase value of 0 and π, respectively.M is an integer, and in some embodiments M=8 or 16. The system may beprogrammed to decide for each phase shift value (0 or π) such that thesummation of phase shifted signals result in more energy at the outputof the combiner (combiner has M inputs). Hereafter, the correspondingvector of size M with elements −1/+1 (determining the respective phaseshifts) is called the Plus-Minus Phase Vector.

In one embodiment, Plus-Minus Phase Vectors used in the formation ofPhysical Signatures are mutually orthogonal (as vectors in an Euclideanspace). This feature reduces the correlation among elements of theSignature Vectors, and thereby improves the accuracy of the underlyinguser identification problem. In a further embodiment, the Plus-MinusPhase Vectors used in the formation of Physical Signatures are fewvectors from a Hadamard basis. Note that Hadamard basis can be realizedas phase shifts are equal to 0 or π, representing multiplication by +1and −1, respectively.

Methods of some of the embodiments described herein may be utilized foruplink beam-forming. An embodiment uses the beam-forming pattern decidedin the uplink to perform downlink beam-forming as well.

To achieve receive beam-forming, some embodiments form a SignatureTable, wherein each entry in this table corresponds to a particularclient node, and client nodes can be identified based on theircorresponding Signature Vectors with a small probability of error. Eachentry (row) in the Signature Table includes several information itemsrelated to its corresponding client node, including the best antennapattern for that particular user. This is in the form of a Plus-MinusPhase Vector, called Best Plus-Minus Phase Vector corresponding to thatparticular client.

The Physical Signatures as well as the stored AWC vectors (e.g., BestPlus-Minus Phase Vector) corresponding to each client will graduallychange as nodes move around, and/or the environment changes. Methodsdescribed herein include updating these signatures and stored AWCvectors. In addition, client nodes leave the system and new client nodesmay join, and the updating procedure described herein accounts for thesephenomena. These procedures may be performed such that the size of theSignature Table remains small to simplify the search. The table isfilled with most recent active client nodes, particularly those clientnodes that are in the desperate need of the beam-forming gain. Themethods of some embodiments described herein account for these featuresby including the age of the table entrees (last time the correspondingclient node was observed and updated), as well as theSignal-to-Noise-Ratio (SNR) of the client in its most recent uplinkconnection.

Once a client node is successfully connected, and after itscorresponding packet is decoded, the access point (AP) will be able toextract the actual identity of the corresponding client in a digitalform, such as its Medium Access Control (MAC) address or its InternetProtocol (IP) address. Hereafter, such identity markers are referred toas a Digital Identity. Methods of some embodiments have a provision forstoring the Digital Identity of the client nodes as an element in theircorresponding row in the Signature Table. This may be used for at leasttwo purposes: (1) to clean up the Signature Table and remove clientnodes who have been inactive for a while, or are not a priority as theirsignal is strong enough, and (2) to decide which beam-forming patternshould be used in the transmit phase (transmit beam-forming). Note that,unlike uplink, in down-link transmission, the identity of the targetedclient is known prior to initiating the over-the-air transmission. Forthe purpose of transmit beam-forming, methods described herein mayextract the Digital Identity of the client to be served next (in thedownlink) prior to initiating the downlink transmission, and accordinglyselecting the corresponding stored beam-forming pattern according to theAWC vector (e.g., in some embodiments a Best Plus-Minus Phase Vectorcorresponding to that particular client).

Note that some measurements, for example channel estimation, will dependon the antenna pattern. Therefore, in some embodiments, the signaturevector is detected, and the corresponding stored AWC vector (i.e., thebest beam forming pattern) should be applied, very early after thereception has started. On the other hand, measurements used fortime/frequency synchronization do not depend on the antenna pattern. Inthe methods described herein, the selected antenna pattern is kept thesame during the preamble used for channel estimation and during all thesubsequent reception from that particular client node (until the uplinkpacket is complete).

For the purpose of receive beam-forming, in an embodiment, signals frommultiple antennas are combined with relative phase shifts that result incoherent (in-phase) addition of signals. It is also possible to selectthe beam patterns to minimize the impact of the interference receivedfrom unwanted neighboring transmitters. Another embodiment uses acombination of these two objectives. On the other hand, for transmitbeam-forming, RF signal transmitted from any given antenna will undergoa phase shift that is the same as the phase shift computed for thatparticular antenna in the receive beam-forming. Due to channelreciprocity, the beam-forming phase values (e.g., Best Plus-Minus PhaseVector) will be effective in both directions (receive and transmit).

As mentioned, some embodiments described herein are directed to WiFisystems. WiFi signaling starts with a Short Training Sequence (STS),followed by a Long Training Sequence (LTS), followed by successive OFDMsymbols. STS is primarily used to: (1) detect the start of an incomingsignal, and (2) to estimate the frequency mismatch between the clienttransmitter and the AP. These measurements are not sensitive to theantenna pattern selection. LTS is the used for channel estimation.Accordingly, methods of some embodiments will perform the following: (1)compute the Physical Signature, (2) perform the matching by searchingthe Signature Table, (3) gather enough information to enable updating ofthe Signature Table, and (4) apply the selected beam pattern (BestPlus-Minus Phase Vector) before the LTS starts.

As mentioned, most techniques will be explained in the context ofreceive beam-forming, while, due to channel reciprocity, same phasevalues (Plus-Minus Phase Vector) can be used for transmit beam-forming.In signalling from a point TX to a point RX, i.e. TX-to-RX, if TX isequipped with transmit beam-forming and RX is equipped with RXbeam-forming, the gains (in dBi) will add.

Many wireless standards rely on multiple antennas. To combine themethods described herein with such standards based on multiple antennas,each legacy antenna is replaced with a configuration of beam-formingantennas explained herein. For example, in a WiFi system based on802.11n standard, APs typically rely on N=4 antennas, each with aseparate receive chain. A typical configuration of this inventionreplaces each of these 4 legacy antennas with a group of M=8 antennasequipped with phase adjustment capability, resulting in 4×8=32 antennasin total. In this case, the Signature Vectors can rely on theinformation extracted from all these 32 antennas. In one embodiment,four different AWC vectors are used to generate four beam-formedsignals, and the signal levels of the training sequences within the fourbeam-formed signals are measured to obtain the Signature Vector.Beam-forming patters (e.g., Plus-Minus Phase Vector for each group ofantennas) will be typically selected to separately maximize the signalsreceived over each antenna. It can also maximize a measure ofperformance that involves all antennas, for example, maximize thedeterminant of the channel matrix which in turn determines the capacityof the underlying multiple antenna wireless system.

Although the methods herein are explained in terms of binary phasevalues (0/180′), it is possible to use a larger number of phase valuesdistributed around the circle, or include the option of turning off thesignal to/from certain antenna(s). Such a construction can be realizedusing transmission line segments of different lengths, and/or lumpedelement circuitries in conjunction with RF switches. If there are “K”options (phase and/or gain) for each antenna and “M” antenna are usedfor beam-forming (in conjunction with each TX/RX chain), then there willbe KM different options available for each TX/RX chain. Subsequently, ifthere are “N” TX/RX chains, there will be a total of KMN options forbeam-forming.

Physical Signatures are “features” of clients' channel and/ortransmitter. In a preferred embodiment (explained so far), averagereceived energy is used as the “signal feature”, but it is possible touse additional features, such as complex gain values over differentfrequency segments, to further enhance the signature vectors.

RX beam-forming patterns are learned and applied prior to decoding theclient's data packet. The use of Plus-Minus Phase Vectors, inconjunction with an efficient search algorithm (tailored to benefit fromthe features of the Plus-Minus Phase Vectors) may be used. A selectedsubset of Plus-Minus Phase Vectors of size S, called Signature Beams(SB), will be used as Plus-Minus Phase values to measure/construct thesignatures. Energy measured over the SBs will be used as SignatureVector (SV). This means, SVs are vectors of size S, with elements thatare energy values, and SBs are vectors of size S, with elements that are−1/+1.

Explanations are primarily presented in terms of the Plus-Minus Phasevalues, formed by creating 180′ phase difference between two RF paths.Other forms of discrete beam-forming strategies include: (1) Using360/2=180 phase increments, or disconnecting any given antenna if itssignal is too weak (three options for each antenna, i.e. K=3). (2) Using360/3=120′ phase increments (three options for each antenna, i.e. K=3).

In an embodiment, different nodes in the network are divided into twosets referred to as “Legitimate Node (LN)” and “Interfering Node (IN)”,which are distinguished using their corresponding signature vectors. TheSignature Table is a dynamic table with each row corresponding to a nodein the network, separated into LNs and INs. Each row includes SV for theparticular node, with auxiliary parameters such as “age”, “best pattern(e.g., Best Plus-Minus Phase Vector) found so far and its measuredenergy level”, “next combination of Plus-Minus Phase Vector to test”,“if the node is LN or IN”, “Digital Identity (MAC and/or IP address) inthe case of LN”, etc. For LN, the Best Plus-Minus Phase Vector isselected/tracked to maximize Signal-to-Noise Ratio (SNR). For IN, theBest Plus-Minus Phase Vector is selected/tracked to minimize theinterference.

It is desirable to implement the instantaneous beam-forming in a mannerthat is transparent to the underlying wireless standard, andconsequently, it can be added to the existing chip sets. In coherentschemes (e.g., using QAM), to maintain the required transparency, TIB isrestricted to complete all its tasks prior to the training signals usedfor channel estimation/equalization. For non-coherent schemes (e.g.,FSK), used in many IOT applications, this restriction is more relaxed.

Following operations are performed over the Signature Table (ST):

(1) Identification Phase: Identify the node based on measuring the SVand comparing it to the SV entries in the ST. The comparison may includedetermining a total or average deviation of the measured features to thestored features in the ST and selecting the ST entry having the lowestdeviation. Once the client node is identified by comparing the set ofmeasured signals to those sets stored in the ST table, the controllerselects a stored beam-former AWC vector based on the set of measuredsignal levels. The selected stored beam-former AWC vector is used toconfigure the beam-former to then process the received signal.

(2) Tracking Phase: Update the corresponding analog weight coefficientvector (e.g., a Best Plus-Minus Phase Vector in some embodiments) bycontinuing the sequential search, starting from the latest “BestPlus-Minus Phase Vector” stored in ST. This phase includes testing L newPlus-Minus Phase Vectors (in one embodiment) and updating the stored AWCvector, or Best Plus-Minus Phase Vector stored in the table if themeasured energies over any of the newly tested Plus-Minus Phase Vectorturns out to indicate improvement. L is selected based on the timeavailable (note that for coherent transmission systems, the“identification phase”, “tracking phase”, and “fixing of the newly foundBest Plus-Minus Phase Vector” should be all completed prior to thearrival of training sequence which will be used for channel measurement(to be used for equalization).

Enhanced Transparent Instantaneous Beam-forming (E-TIB): So far, methodsdescribed herein have been explained when beam-forming is used at the APand clients are legacy units without any modifications in theirstructures. In such setups, the link quality is enhanced, while clientsremain transparent to its operations. In other words, client nodes enjoya better connection without the need to modify their hardware/software,nor their signaling structure. On the other hand, in some scenarios suchas backbone wireless coverage or last mile applications, both ends ofthe wireless connection can be modified as long as both ends adhere tothe changes. In another embodiment, such setups are further enhanced byinserting (or superimposing) a Signature Signal within the legacy signalstructure, which will be in turn detected by the receiving end and usedto distinguish the transmitted signal as belonging to the network, andpossibly even extract the identity of its transmitting node, in a timelymanner. Hereafter, this is called the Enhanced Transparent InstantaneousBeam-forming (E-TIB), in contrast to the base embodiment without thisfeature which was referred to as Transparent Instantaneous Beam-forming(TIB). In some embodiments of E-TIB, any signal that does not containthe added signature will be classified as interference, which in turnwill be nullified in the process of finding the antenna beam patters(Best Plus-Minus Phase Vector). In these embodiments, the beam-formingalgorithm will maximize the signal strengths from/to nodes of the samenetwork, and at the same time, will minimize the effect of theinterference observed from neighboring units (such units will not havethe inserted Signature Signal). Added signature signals can be separatefrom the legacy signal in frequency, time or code domains. Examples forthe added Signature Signals include: (1) Transmitting a sinusoidalsignal in parts of the signal spectrum that is left unoccupied (such asthe frequency range near DC or near the edges of the band). (2)Transmitting an additional preamble prior to the start of the legacypreamble. (3) Superimposing a low power spread spectrum signal on top ofthe legacy signal.

In OFDM based standards such as WiFi, the portion of spectrum around DC(which upon RF up-conversion maps to spectrum around carrier) is leftempty. In some embodiments of E-TIB, a low frequency signal is modulatedonto the RF carrier and combined with the outgoing RF signal at the RFfront-end. This signal is transparent to legacy nodes, while receivingnodes with E-TIB capability can extract and use it to identifyLegitimate Nodes, vs. Interfering Nodes. This feature enables separatingInterfering Nodes from Legitimate Nodes in a reliable and fast manner.Another option for the insertion of a Signature Signal include formationof a low power, wideband signal (spread spectrum) and combining it withthe transmitted signal. It is also possible to insert the addedsignature signal prior to the start of the legacy preamble.

In another embodiment, the Signature Signal embedded in the RF signal inE-TIB carries information to be added to the Signature Vector and usedin distinguishing/separating Legitimate Nodes. Information regardingDigital Identity of the transmitting node can be embedded in theinserted signature signal using simple modulation strategies, inparticular differential binary phase shift keying may be used in someembodiments.

In the WiFi standards, the available bandwidth is divided into multiplesub-channels. In this case, the wireless network in which both ends areequipped with E-TIB signaling methods will switch between differentsub-channels for the purposes of limiting their impact on other linksthat are not part of their setup.

Using Two Sets of Phase Shifters to Enable Parallel Training: So far,methods have been explained in terms of using M antennas per chain, eachequipped with its own phase rotation unit. To further improve theperformance, in another embodiment, the set of antennas are connected totwo separate sets of phase shifter units, A and B, each of size M. Moregenerally, each set of antennas may have two sets of analog weightcoefficient multiplier elements to form two separate beam-formedsignals. One set of phase shifters, say A, at the end of the STS (uponcompletion of its standard training phase) will feed the beam-formedsignal to the receiver chain to be decoded, while the other set, B,continues to undergo an enhanced training phase by examining furtherpatterns. During the enhanced training phase of B, the system can: (1)Examine more patterns for the legitimate client, that, at the time, isunder service over set A (in order to find a better pattern for the nexttime that client connects over B), and/or (2) Discard some patterns thatresult in high interference from interfering nodes that are likely to beactive in the immediate future. Interfering nodes can be followed bylistening to any incoming preamble signal throughout the enhancedtraining phase of set B, which will be necessarily from an interferer(as, at that time, the channel is occupied by a legitimate client overset A and other legitimate clients do not transmit). In the case ofWiFi, this entails detecting further occurrence(s) of the STS during theenhanced training phase over B. This is achieved by computing theautocorrelation over sliding windows of size 16 (see FIG. 8 for STS),and examining the peaks. This feature allows the beam-former tocontinually follow interfering nodes as part of the enhanced training ofset B without disturbing the main reception, which will be concurrentlyunder progress over set A (after completion of A's standard training).This feature provides the beam-forming algorithm operating over set Bwith a longer observation window towards making better decisions (forenhancing signal strength and/or for reducing interference). Inparticular, the system, upon detecting an interferer, may test thecurrent AWC vector for the desired legitimate client and additionalcandidate AWC vectors, and remove those that produce features (such ashigh energy) associated with the interfering signal. Note: It is likelythat the same client and the same interferer will continue in theimmediate future (due to the bursty nature of WiFi) and it helps tomonitor which patterns are better in terms of improving signal andreducing the interference, because it is reasonable to assume that thesame legitimate client and interfering node will become active once gainin the immediate future.

The phase shifter set under enhanced training (set B) and the one withstandard training (set A), which is used to feed the receiver at the endof the STS of the legitimate client, will switch their roles accordingto a pre-programmed periodic schedule, or as the underlying controlstructure deems necessary. This means, at any given time (say at eventimes), one of the two sets undergoes the enhanced training phase, whilethe other set will be connected to the RF input (after the standardtraining prior to the end of STS).

Transmit Beam-forming: many of the techniques discussed so far have usedthe ability to identify nodes in a fast manner, i.e., prior to the startof their data carrying signal and its associated training signals. Thisfeature enables identifying the nodes prior to demodulating theirsignals, i.e., prior to extracting their Digital Identity captured intheir digital (MAC/IP) address. On the other hand, in transmit mode, theDigital Identity will be available prior to starting the wirelesstransmission phase. This feature will be used to select the BestPlus-Minus Phase Vector for the transmit phase, which according toreciprocity principle, will be the same as the Best Plus-Minus PhaseVector of the corresponding client extracted in the receive mode.

Cleaning of the Signature Table (ST): To avoid overflow of the SignatureTable, and improve the accuracy of client identification, redundantentries may be removed or given less priority in the search. Examplesincludes duplicates, nodes which have left the network, nodes that haveaged and need to be refreshed, and Interfering Nodes that are classifiedby mistake and Legitimate Nodes. An algorithm (Table CleaningAlgorithm-TCA) will run in parallel with the reception phase. TCA hasless constraints on “execution-speed” and “time-to-finish”. TCA comparesthe signatures and considers all entries' age-values to decide aboutcombining entries or removing the old ones, and removing the entriesthat are not part of the network (have been included by mistake). TCAcan rely on the Digital Identity of the node (MAC/IP), which will beavailable with delay (after the packet is decoded), to prune the tableand/or to merge multiple entries through combining or simply replacingduplicate entries by one of them, typically the most recent one. TCAbenefits from side information such as “acknowledgement” and “MAC/IP”address.

Auxiliary Receiver as a Finite State System: The status of the AuxiliaryReceiver is categorized in terms of several states. Examples of some ofthe states are provided next. The explanations are provided in thecontext of WiFi, and similar line of definitions and strategies would beapplicable to other standards. The actual implementation will not belimited to the set of states described below, but othervariations/extensions may be made. In addition, the number, definitionand the role of states may change from scenario to scenario, for exampledepending on the environment (residential, enterprise, indoor,out-door), level of interference, type and volume of traffic, etc. Thismeans the state diagram adapts to the situation. The reason for makingsuch a state diagram adaptive is to capture the impact and significanceof these different factors in its underlying decision-making processes.

-   -   Idle State: Receiver is listening and looking for an incoming        preamble (peak in the STS correlator), while measuring the        energy level, which is obtained by averaging the sample energy        values over several, say 100, consecutive samples with a moving        average, or other known techniques, for smoothing and noise        reduction.    -   Note: While in idle state, the Auxiliary Receiver changes the        beam-forming patterns (Plus-Minus Phase Vectors) with the        objective of finding a subset of patterns that would reduce the        noise floor of the system. This subset will have a higher weight        in following stages of decision-making for selecting the Best        Plus-Minus Phase Vector (best pattern) for each Eligible Client.    -   Active State: Receiver has detected a preamble (peak in the STS        correlator), but the end of the packet is not reached. End of        the packet is identified by a combination of the following        criteria:        -   1. Energy level falls below certain threshold, wherein            energy level is obtained by averaging the sample energy            values over several, say 100, consecutive samples with a            moving average, or other known techniques, for smoothing and            noise reduction.        -   2. Energy level has already fallen and legacy AP has sent an            acknowledgment.        -   3. Energy level has already fallen and legacy AP has            successfully decoded a packet.    -   Note: While in the Active State, the Auxiliary Receiver        continues to search for incoming preambles, while the pattern is        kept fixed (if there is a single set of beam-formers), or        changed to gather more information (if there are two sets of        beam-formers, and for the set that is under Enhanced Training).    -   Doubly Active State: Receiver has detected a preamble (peak in        the STS correlator), but before detecting the end of packet, a        second preamble is detected.    -   Error State: Auxiliary receiver is in the idle state, but legacy        receiver generates an acknowledgement and/or detects a packet        (with CRC failed or passed).

Rules Concerning Transitions Between States and the AssociatedDecision-Making Process:

These rules and decision-making procedures are not the same for allsituations. These rules are typically adapted to the setup, e.g., basedon the (1) amount of possible handshaking with the underlying legacyWiFi receiver, (2) amount of interference in the environment, (3)general behaviours of Eligible Clients and Interferers, for example thetype of traffic and physical environment (if it is a residentialnetwork, enterprise network, indoor, outdoor, etc.), (4) if theauxiliary receiver is equipped with two phase shifter units, or onlyone, (5) if the setup is E-TIP or simply TIP, (6) carrier frequency andbandwidth (e.g., if the channel is 20 MHZ, 40 Mhz, or 80 Mhz in802.11AC), (7) number of chains in the legacy receiver and its mode ofoperation (MIMO with multiplexing gain, MIMO with diversity gain, and ifthe AP is relying on Spatial Division Multiplexing of clients, or not,(8) statistics of the number of retransmissions in the network, and (9)availability SINR measurements’, latency, etc., reported by theunderlying legacy AP. Next, some examples are provided for some of themore important decision-making procedures.

Decisions and their Criteria:

In some embodiments, there are two tables for clients: (1) Table ofEligible Clients and (2) Table of Interferers. The Auxiliary Receivermay make a number of decisions concerning these two tables, with asummary of some of the more important ones provided below.

-   -   Decision 1: Delete an entry from the Table of Eligible Clients.    -   Decision 2: Delete an entry from the Table of Interferers.    -   Decision 3: Move an element from Table of Eligible Clients to        Table of Interferers, or vice versa.    -   Decision 4: Search to improve the best pattern for the current        client (detected in the current Active State). Update the        corresponding entry in the Table of Eligible Clients. Select and        fix the pattern.    -   Note: In the case of having two sets of phase shifters, the beam        pattern will be fixed only over the set that is connected to the        legacy receiver, and the second set (under extended training)        can continue examining more patterns and record its        observations.    -   Decision 5: Update the attributes associated with rows in both        tables. Example of attributes for the Table of Eligible Clients        include: (1) age, (2) best pattern, (3) bit positions flipped in        the previous search for the best pattern for that client,        and (4) Digital Entity. Example of attributes for the Table of        Interferers include: (1) age, (2) energy level over a number of        previously examined patterns and their corresponding binary        phase vectors, and (3) bit positions flipped in the previous        energy measurement for that interferer.

Decision Making Procedures:

-   -   Decisions 1, 2, 3 are performed using a weighting mechanism        involving the underlying criteria. The weighting mechanism is        adjusted to account for the state of the Auxiliary Receiver, and        relevant attributes such as “energy level” and “age”.    -   Decision 4: Before the end of the STS, the Auxiliary Receiver        has time to examine 7 different patterns. Four of these will be        the ones forming the signature vectors, which are fixed. Then,        three more patterns are tested by flipping bit positions in the        Plus-Minus Phase Vector. The bit flipping is performed scanning        through consecutive bit positions in a circular manner (wrapping        around to the first bit, once the last bit is flipped and its        effect is measured). Position of the bit flipped in the previous        detection of that particular client is tracked and stored as an        attribute of the corresponding row in the Signature Table. Upon        flipping a bit, if the measured energy level shows improvement,        the bit will be kept in the flipped position; otherwise, it will        be flipped back. In each new round of bit flipping, the bits are        flipped continuing from the bit position stored in the Signature        Table, which identifies up to which bit position has been        previously flipped/tested for that particular client. Overall,        in each round, 7 patterns are tested (four for signature        extraction and three in searching for a better pattern), and        then the best among these 7 will be selected and the Table of        Signatures will be updated accordingly.

System Firmware Adaption: The methods described herein includeprovisions for (automated) dynamic adaptation of various rules anddecision-making procedures. Algorithms running within the hardware ofthe Auxiliary Receiver will execute these operations. A central computercan gather the information from all the active APs and new updatingalgorithms can be designed off-line by considering the behaviour andperformance of the various AP into account, while considering theirenvironments (residential, vs. enterprise, etc.), and if the AP is TIP,or E-TIP. The corresponding algorithms can be modified through automatedupgrade of the system firmware.

Monitoring Individual Antennas in Addition to their Combined Signal: Inthe methods described above, the Auxiliary Receiver has been monitoringthe output of the combiner related to each legacy RF chain. In anotherembodiment, in addition to the output of the combiner, the outputs ofindividual antennas can be monitored towards extracting informationabout the individual signals separately. This information, for example,can be used towards deciding to adjust the gain/attenuation ofindividual antennas according to their noise level. An extreme casewould be to decide to turn off a particular subset of antennas. Apictorial view of such a configuration is shown in FIG. 18, wherein twoseparate Auxiliary Receivers are deployed for this purpose (forpresentation simplicity, only 4 antennas per each receive chain areshown in FIG. 18).

Sharing of Auxiliary Receiver(s) (Time Multiplexing among DifferentTasks): In another embodiment, a single Auxiliary Receiver is shared(time multiplexed) between these different measurement/monitoring tasks.A pictorial view of such a configuration is shown in FIG. 19 (forpresentation simplicity, only 4 antennas per each receive chain areshown in FIG. 19).

In another embodiment, the Auxiliary Receiver is shared (timemultiplexed) between the tasks associated with beam-forming fordifferent legacy RF chains. A pictorial view of such a configuration isshown in FIG. 20.

Application in Non-coherent Signaling: Coherent transmission schemes,such as OFDM, rely on channel measurements using training signals forthe purpose of equalization. On the other hand, in non-coherent schemes,which are gaining renewed attention in IoT applications, adjustment ofantenna beams, formation of “Signature Table” and “Cleaning of theSignature Table” can be partially performed during the signal reception.

FIG. 1 shows a pictorial view of an embodiment of this invention whereinthe access point is equipped with receive beam-forming in a manner thatthe beam-forming operation is completely transparent to legacy clients.

FIG. 2 shows the structure of a general receive beam-forming apparatuswherein each of the K receive chains is equipped by M antennas, andwherein signals received by the M antennas in each of these K groups arecombined after application of complex gains (called antenna beam-formingweights) to adjust their relative magnitude/phase, and the result is fedto the RF input of the corresponding legacy receive chain.

FIG. 3 shows a preferred embodiment of this invention for theimplementation of antenna beam-forming weights, wherein only the signalphase is changed by 180′, while signal magnitude remains the same.

FIG. 4 shows a pictorial view of the beam-forming apparatus with itsassociated control unit.

FIG. 5 shows pictorial view of a preferred embodiment of this inventionfor generating 0/180 degrees phase shifts.

FIG. 6 shows pictorial view of another preferred embodiment of thisinvention wherein 0/180 degrees phase shifts are cascaded with RFattenuators to provide some additional degrees of freedom in adjustingantennas beam-forming weights.

FIG. 7 shows an example of Plus-Minus Phase Vectors used in theformation of Physical Signatures corresponding to M=8 (# ofantennas/chain), K=1 (# of chains), and S=4 (# of signature vectors).Total number of antenna patterns is 28=256.

FIG. 7 shows an embodiment of this invention wherein each group of Mantennas is equipped with two sets of beam-formers, wherein at any giventime (say at even times), one of these sets is being trained while theother set is used to fed the corresponding RF input of the underlyinglegacy receiver.

FIG. 8 shows a pictorial view of the WiFi preamble, indicating theoperations that need to be completed prior to the start of the LongTraining Sequence (LTS), such that channel measurements are performedfor the actual antenna configuration that will be in effect. ShortTraining Symbols may comprise 10 repetitions of a sequence of length 16.Such sequences may be used for signal detection, time synchronization,and frequency offset measurement. FIG. 8 also shows one embodiment ofthe latest finalization time, which is the latest time that theextraction and matching of a signature vector, updating of a signaturetable, and selection of an antenna beam pattern may be finalized.

FIG. 9 shows another embodiment wherein each group of M antennas isequipped with two sets of phase shifters operating in parallel, whereinone of the sets is connected to the legacy receiver at the end of theSTS (upon completion of its standard training phase), and the other setcontinues to undergo an enhanced training phase by examining furtherpatterns for the legitimate client (under active service by the otherset), or by discarding patterns that would result in high interference.At any given time (say at even times), one of the two sets undergoes theenhanced training phase, while the other set will be connected to the RFinput (after its standard training, prior to the end of STS).

FIG. 10 shows a pictorial view of the switching between the twobeam-forming sets related to FIG. 9.

FIG. 11 shows the pictorial view of a network setup equipped withEnhanced Transparent Instantaneous Beam-forming.

FIG. 12 shows another embodiment wherein each group of M antennas isequipped with two sets of beam-former phase shifters operating inparallel, wherein one of the sets is connected to the legacy receiver atthe end of the STS (upon completion of its standard training phase), andthe other set continues to undergo an enhanced training phase byexamining further patterns for the legitimate client (under activeservice by the other set), or by discarding patterns that would resultin high interference. At any given time (say at even times), one of thetwo sets undergoes the enhanced training phase, while the other set willbe connected to the RF input (after its standard training, prior to theend of STS). The formation and updating of the signature tables isenhanced relying on the digital ID of the node being received with delayupon completion/decoding of the received packet from the networkinterface, plus the information gathered from what is embedded in thesuperimposed signature signal in the case of using Enhanced TransparentInstantaneous Beam-forming.

FIG. 13 shows a pictorial view of a preferred embodiment of thedisclosed Enhanced Transparent Instantaneous Beam-forming structure forsuperimposing a sinusoidal signature signal on the RF signal generatedby the underlying legacy transmitter. FIG. 13 also shows a sinusoidalsignal (indicated as “sinusoidal signal”) with a frequency falling in anunoccupied portion of the legacy spectrum, such as near DC or at afrequency band's edges (or frequency guard band).

FIG. 14 shows a pictorial view of a preferred embodiment of thedisclosed Enhanced Transparent Instantaneous Beam-forming structure forsuperimposing a sinusoidal signature signal containing modulated data onthe RF signal generated by the underlying legacy transmitter. Apreferred embodiment relies on differential Binary Phase Shift Keying toembed data in the superimposed signature. This data is used tocommunicate a digital identifier (which can be extracted/decoded priorto the end of STS) specifying the node being active. FIG. 14 also showsa sinusoidal signal (indicated as “sinusoidal signal”) modulating a lowrate binary signal with a modulated frequency range falling in anunoccupied portion of the legacy spectrum near DC. A low rate binarysignal contains information related to the node, e.g., a pre-arranged IDnumber, which may be used by the receiver in determining a proper beampattern. FIG. 14 shows the sinusoidal signal as an input to a bandpassfilter centered at the carrier frequency.

FIG. 15 shows a pictorial view of a preferred embodiment of thedisclosed Enhanced Transparent Instantaneous Beam-forming structure forsuperimposing a spread spectrum signature signal on the RF signalgenerated by the underlying legacy transmitter. The RF switches in FIG.15 in essence generate a Binary Phase Shift Keying signal with apre-programmed bit pattern and use it as the superimposed signature. Theexample demonstrates the use of a periodic Alexis sequence as thespreading sequence. A preferred embodiment relies on differential BinaryPhase Shift Keying to embed data in the superimposed spread spectrumsignature signal. This data is used to communicate a digital identifier(which can be extracted/decoded prior to the end of STS) specifying thenode being active. FIG. 15 shows a switch (indicated as “switch”) forselecting one of two ends of the secondary phase shift, which may be 0°or 180°. For one embodiment, the secondary phase shift is programmed togenerate a periodic alexis sequence, which may be a repetition of thefollowing expression: “[−1 −1 −1 −1 +1 +1 +1 −1 +1 +1 −1 −1 −1 −1 +1 −1+1 −1 −1 −1 −1 −1 +1 +1 −1 +1 +1 +1 −1 −1 −1 −1].” One side of theswitch may be connected as an input to a bandpass filter (indicated as“bandpass filter” in FIG. 15) centered at the carrier frequency. Theoutput of the bandpass filter, which is indicated as “bandpass filteroutput” and is connected to an RF coupler, may be a signal with binaryphase shift keying and periodic repetition of a low correlationsequence, such as an alexis sequence.

FIG. 16 shows the pictorial view of the control mechanism in EnhancedTransparent Instantaneous Beam-forming.

FIG. 17 shows the procedure in changing the selected channel for thereason of limiting the impact on other users who are sharing thespectrum and are not part of our network, i.e., do not contain oursuperimposed signature signal.

FIG. 18 shows an embodiment wherein, in addition to the output of thecombiner, the outputs of individual antennas are monitored towardsextracting information about the individual signals separately.

FIG. 19 shows a pictorial view of an embodiment for sharing theAuxiliary Receiver.

FIG. 20 shows a pictorial view of another embodiment for sharing theAuxiliary Receiver.

1. A method comprising: at a wireless receiver: detecting a receivedtransmission frame having training signals; determining that thereceived transmission frame has an associated signature signal, andresponsively categorizing the received signal frame as a desired frame,and otherwise categorizing the received signal frame as an interferenceframe; identifying one or more beam-forming analog weight coefficientvectors that when applied to an analog beam former operating on desiredframes enhances a signal strength of the training signals and that whenoperating on an interference frame reduces the signal strength of thetraining signals; storing the one or more identified beam-forming analogweight coefficient vectors; configuring the analog beam-former with oneof the identified beam-forming analog weight coefficient vectors andprocessing subsequently received desired frames.
 2. The method of claim1 wherein the signature signal is a carrier signal transmitted in afrequency range unused by the desired frame.
 3. The method of claim 1wherein the signature signal is a network preamble signal located priorto the training signals.
 4. The method of claim 1 wherein the signaturesignal is a spread-spectrum signal superimposed on the desired frame. 5.The method of claim 1 wherein the desired frame is formatted accordingto an orthogonal frequency division multicarrier (OFDM) signal, and thesignature signal occupies a subcarrier located substantially near acarrier frequency.
 6. The method of claim 1 wherein the signature signalcomprises a digital identity of a source of the desired frame.
 7. Themethod of claim 6 wherein the digital identity is modulated onto thesignature signal using binary phase shift key signaling.
 8. The methodof claim 1 wherein each of one or more beam-forming analog weightcoefficient vectors comprise vector elements, and wherein each vectorelement is selected from a set of 0° and 180°.
 9. The method of claim 1wherein the analog beam former comprises a plurality of baluns.
 10. Themethod of claim 9 wherein each balun of the plurality of baluns canselectively provide a received signal or a phase shifted version of thereceived signal.
 11. A method comprising: at a transmitter: generating atransmit data frame according to a wireless network protocol, whereinthe data frame includes training signals; generating a signature signalindicating that the transmit data frame has been formatted according toan instantaneous beam forming protocol; and, combing the transmit dataframe and the signature signal at a radio frequency combiner prior totransmission.
 12. The method of claim 11 further comprising: receiving acontrol signal indicating a preferred analog weight coefficient vector,wherein the transmit data frame is transmitted according to thepreferred analog weight coefficient vector.
 13. The method of claim 11wherein the signature signal is a carrier signal transmitted in afrequency range unused by the transmit data frame.
 14. The method ofclaim 11 wherein the signature signal is a network preamble signallocated prior to the training signals.
 15. The method of claim 11wherein the signature signal is a spread-spectrum signal superimposed onthe transmit data frame.
 16. An apparatus comprising: a configurablebeam-former having a plurality of radio frequency signal inputs andhaving a control input for controlling a plurality of adjustable weightelements to generate a beam-formed signal based on a plurality ofreceive signals obtained from the plurality of radio frequency signalinputs; a receiver configured to receive training signals and to detectthe presence or absence of a signature signal; a beam-former controllerconfigured to provide a plurality of identifier control inputs to theconfigurable beam-former during a transmission identification period; aprocessor configured to generate a set of training signal measurementswithin the beam-formed signal during the transmission identificationperiod, each training signal measurement of the set of training signalmeasurements corresponding to a beam-formed signal generated in responseto a corresponding control input of a plurality of control inputs,wherein the set of measurements is associated with an indicatorindicating the presence or absence of a signature signal; and abeam-former selector configured to select a previously stored analogweight coefficient (AWC) vector that corresponds to the set of trainingsignal measurements generated by the training signal processor, theselected previously stored AWC vector to be used in configuring theconfigurable beam-former when the receiver has detected the presence ofa signature signal.